This invention relates generally to force generators and force generating methods used downhole in a well, such as an oil or gas well. A particular aspect of the invention is its automated control which enables varying degrees of different states of operation to be obtained. For example, a particular embodiment of the invention provides for variable control of fluid flow through an "infinitely" variable choke that is operated across a continuum of "openness" or "closedness" as distinguished from merely one open state and one closed state.
Although the present invention can be used in any type of borehole in which the usefulness of the invention is needed, it will be described with reference specifically to an oil or gas well. In drilling, testing, completing and producing such a well, many different types of equipment can be used in the well. Some of this equipment is operated by a force applied to the equipment. For example, a valve is one type of equipment typically used in an oil or gas well, and a force typically needs to be applied to the valve member to rotate or slide it between fully closed and fully open positions.
Different types of forces may be needed to accomplish the foregoing. One example is a hydraulic force exerted by a fluid under pressure. Another example, and the one relevant to the present invention, is a mechanical force exerted by one structural body moved relative to another structural body. Such force can act in different directions. In a preferred embodiment of the present invention, the force acts longitudinally relative to the well. An example of a longitudinally acting force generating apparatus is shown in U.S. Pat. No. 5,492,173 to Kilgore et al.
A shortcoming of the apparatus disclosed in the Kilgore et al. patent is that it does not have the ability to variably control itself. The Kilgore et al. apparatus provides a longitudinal force to operate a device down in a well; however, the Kilgore et al. patent does not disclose a programmed downhole controller to control the apparatus across a continuum, or to different degrees, of one or more general states. With regard to fluid flow, this control is desirable such as for obtaining different flow rates or for maintaining a constant flow rate even as a flow control orifice of the downhole device being operated deteriorates because of an abrasive fluid flowing through it. Thus, there is the need for a downhole force generator and a downhole force generating method by which variable control of a downhole operated device can be obtained. Preferably such control should be obtained automatically, such as to implement a single event or a preprogrammed sequence, and at relatively low cost.